Making tetraethyl lead



United States Patent 3,048,611 MAKENG TETRAETHYL LEAD Laszlo F. lliritz,Chicago, Ill., assignor, by mesne assignments, to Houston ChemicalCorporation, New York, N.Y., a corporation of Texas N0 Drawing. FiledNov. 24, 1961, Ser. No. 154,817 6 Claims. (Cl. 260--437) It has beenproposed in Pagliarini U.S. Patent 2,848,- 471, August 19, 1958, tocatalyze this reaction with various aryl or mixed aryl alkyl phosphates.The minimum reaction time in Pagliarini is 60 minutes.

It is an object of the present invention to provide a process ofpreparing tetraethyl lead in a shorter time than that disclosed byPagliarini.

Another object is to utilize a lesser weight of catalyst than thatemployed by Paglian'ni, while at the same time obtaining at least anequal catalytic efiect.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications Within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

It has now been found that these objects can be attained by reacting alead-sodium alloy with ethyl chloride in the presence of a small amount,e.g., 0.002%, based on the moles of sodium in the lead-sodium alloy of atrialkyl phosphate having 1 to 4 carbon atoms in the alkyl groups. Thepreferred alkyl phosphates do not have over 3 carbon atoms in the alkylgroups.

While preferably lead-monosodium alloy is employed, there can be usedother lead-sodium alloys such as Na Pb and Na Pb The sodium can be 5-20%of the alloy by weight. The ethyl chloride and lead-sodium alloy can. bereacted on an equimolar basis. an excess of the ethyl chloride is used,e.g., 1.3- moles per mol of lead-monosodium alloy, to obtain betteryields.

Examples of suitable trialkyl phosphates which can be used asaccelerators are trimethyl phosphate, triethyl phosphate, dimethyl ethylphosphate, tripropyl phosphate, triisopropyl phosphate, tribu-tylphosphate, tri secondary butyl phosphate and tri tertiary 'butylphosphate.

The savings in catalyst over those disclosed in Pagliarini will beapparent when it is realized that there need be used in place oftriphenyl phosphate (the simplest triaryl phosphate) only as muchtrimethyl phosphate, 59% as much triethyl phosphate, 72% as muchtripropyl phosphate and 86% as much tributyl phosphate. The preferredmaterial in Pagli-arini is tricresyl phosphate, since he employs it inall of his examples. Based on tricresyl phosphate there need be usedonly 76% as much tributyl phosphate, 64% as much tripropyl phosphate,52% as much triethyl phosphate and 40% as much trimethyl phosphate.

The lowest molecular weight compound mentioned by However, preferablytook 35-38 minutes to obtain a total yield of about 95% about 7073 C. inthese runs.

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2 Pagliarini is dibutyl phenyl phosphate. There can be used 93% as muchtributyl phosphate and 78% as much tripropyl phosphate to obtain anequivalent catalytic effect. While Pagliarini always considered itnecessary to have an aryl group present the present invention ispredicated on the fact that the aryl grouping can be omitted and anequivalent or better catalytic effect obtained utilizing less weight ofcatalyst and an attendant savings in cost.

The examples were carried out using the following conditions. A 150 ml.stainless steel bomb was purged with nitrogen (an inert atmosphere).Then 46 grams of leadmonosodium alloy (0.2 mol) of 12-24 mesh size wereplaced therein. The particle size of the alloy is conventional and isnot critical. (Thus it can be widely varied, e.g., from 4 to 300 mesh.)The bomb was evacuated to about 1 mm. or less and put in a DryIce-acetone bath and then there were condensed in the bomb 80 grams ofethyl chloride. (This is a substantial excess of the ethyl chloride overtheoretical and can be varied, for example between 70 and grams, withoutsignificant change in yields.) The bomb was then pressured with nitrogento 10 p.s.i above atmospheric pressure. The alkyl phosphate catalyst(accelerator) was then put in the cold mixture and the bomb placed in ashaker bath maintained at about 70 C. It took about 3 minutes for thebomb to get to bath temperature. In the examples, in recording the time,the time to reach bath temperature is included. Hence the reaction timeat the bath temperature was actually somewhat less than the timesstated.

It may be noted that the temperature of reaction is not critical but canbe varied, e.g., from 50-120" C.

In the examples total yield was obtained by determining the amount ofsodium chloride formed and yield of tetraethyl lead (T.E.L.) wasdetermined by iodine titration.

As previously indicated in the examples, the alloy employed waslead-monosodium alloy.

A series of controls were run, omitting the catalyst. 1t

and a T.E.L. yield of about 76% at a temperature of Approximately 18-20%of the total yield was by-product, rather than the desired tetraethyllead.

Example I The catalyst employed was 0.728 grams of triethyl phosphateand the temperature was 70.2-70.6 C. There was a total yield of 95.5%and a T.E.L. yield of 84.8% in 21 minutes. This was a material reductionin time for completion of reaction and also was a reduction in sidereaction from the 18-20% down to 11.16%. In contrast, certain othercatalysts e.g., tetraethyl ortho silicate and acetone while reducing thetime of reaction do not reduce the amount of side reaction.

When 1.408 grams of tn'cresyl phosphate were em-' ployed in place of thetriethyl phosphate there was a total yield of 89.1% and a T.E.-L. yieldof 71.54% in 27 minutes. The main reaction was about 80.3%. Thus withalmost twice as much tricresyl phosphate it took a longer time to obtaina yield comparable to that obtained with the triethyl phosphate.

Example 11 presence of a trialkyl phosphate having 1 to 4 carbon atomsin the alkyl groups as a catalyst.

2. A process according to claim 1 wherein the catalyst is present in anamount of 0.002-5 mol percent based on the sodium in the alloy.

3. A process according to claim 2 wherein the leadsodium alloy islead-monosodium alloy and the ethyl chloride is used in an amount inexcess of that required to react with the alloy.

4. A process of preparing tetraethyl lead comprising 10 reacting alead-sodium alloy and ethyl chloride in the presence of trimethylphosphate as a catalyst.

5. A process of preparing tetraethyl lead comprising reacting alead-sodium alloy and ethyl chloride in the presence of triethylphosphate as a catalyst.

6. A; process of preparing tetraethyl lead comprising reacting alead-sodium alloy and ethyl chloride in the presence of a tripropylphosphate as a catalyst.

No references cited.

1. A PROCESS OF PREPARING TETRAETHYL LEAD COMPRISING REACTING ALEAD-SODIUM ALLOY AND ETHYL CHLORIDE IN THE PRESENCE OF A TRIALKYLPHOSPHATE HAVING 1 TO 4 CARBON ATOMS IN THE ALKYL GROUPS, AS A CATALYST.